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Cylichna ordinaria E.A. Smith, 1891

Description: Shell elongate, involute, width about 43% of total shell length. Apex without umbilicus. Last whorl with sides weakly convex. Shell surface smooth, without spiral sculpture. Aperture narrow over top 2/3 of shell, wide at bottom; outer lip sharp (broken in figured specimen). Columella with moderately strong plait, with callus expanded onto base. Parietal wall with thin callus. Shell white.

Size: Up to 7 mm in length.

Distribution: Known only from off Sydney and Wollongong.

Habitat: Subtidal. Holotype from Challenger station 164B, from 410 fathoms (750 m) off Sydney. Other specimens are from 457 and 1463 m off Sydney and 1190-1244 m off Wollongong.

Comparison: This is like Cylichna thetidis, but is shorter and stouter and lacks an apical umbilicus. It also occurs from deeper water.

Remarks: There are only three lots of this species in the Australian Museum collection. These are from off Sydney and Wollongong, but the distribution is probably much wider. A similar species, Volvulella truncata Dell, 1956, is from deep water off New Zealand and may be the same species.

Fig. 1: 27 miles (44 km) off Sydney, in 457 m (C.24469). A label with this specimen says "Compared in British Museum and found correct by H.R. Preston, Sept. 1912".


Copyright Des Beechey 2018